Flame-retardant resin, composition thereof, and process for producing the same

ABSTRACT

A flame-retardant resin composition comprising a phosphazene flame retardant and a polyester resin, wherein the flame retardant is bonded to the molecules of the polyester resin via the ester group thereof, can retain a high flame retardance for a prolonged term with little or no vaporization with time and is excellent in flame retardance, impact resistance, properties and processability.&lt;/PTEXT&gt;

This application is the National Stage Application of PCT/JP99/01169filed Mar. 11,1999.

TECHNICAL FIELD

The present invention relates to a flame-retardant resin composition anda process for preparing the same, and more particularly to ahalogen-free flame-retardant resin prepared by reacting a reactivephosphazene compound as a flame retardant with a polyester resin toimpart remarkably increased flame retardance to the resin withoutvaporization or loss, a composition thereof and a process for preparingthe same.

BACKGROUND ART

Because of their superiority in moldability, mechanical properties,electrical characteristics and appearance, plastics are useful asmaterials for office automation equipment such as computers, wordprocessors, printers and copying machines, electrical appliances such astelevision sets, videos and game machines, and communications equipmentsuch as telephones and facsimile machines. However, plastics have adrawback of being more flammable than metal materials and inorganicmaterials. From the viewpoint of safety, there is an increasedworld-wide demand for making plastics flame-retardant, and regulationswere tightened. A variety of methods have been proposed for renderingflammable plastics flame-retardant. Generally the proposed methodscomprise mixing plastics with a chlorine compound, a bromine compound orlike halogen compounds capable of producing a high flame retardanteffect. It is also known to achieve a synergistic flame retardant effectby further adding antimony oxide in the method. Useful bromine compoundsinclude, for example, decabromodiphenyl ether, tetrabromobisphenol-A,brominated phthalimide and like nuclear bromine-substituted aromaticcompounds. The addition of these excellent flame retardants imparts ahigh flame retardance to plastics but poses the following problems: theimpact resistance is decreased and heat deformation temperature islowered; the flame retardant bleeds out on the surface of plasticsmoldings, resulting in impaired appearance of the moldings; and the moldand screw are eroded in the presence of a decomposition gas of halogencompound in the molding process. Also undesirable from safety andhygiene viewpoints is poison generated from a low-molecular-weightbromine compound or chlorine compound when plastics are processed orburned. In this background, it has been desired to provide aflame-retardant resin composition substantially free of a bromine orchlorine compound or like halogen compounds.

Known methods of rendering plastics flame-retardant without use of ahalogen compound include methods wherein plastics are mixed with aninorganic metal hydroxide such as aluminum hydroxide or magnesiumhydroxide (JP-A-51-132254, JP-A-56-136832 and JP-A-60-13832). However,the methods require a large amount of the inorganic metal hydroxide togive satisfactory degree of flame retardance, and have a shortcomingthat the inherent properties of plastics are lost.

On the other hand, prior art literature disclose techniques forimparting flame retardance without using such inorganic metal hydroxidewherein plastics are mixed with a phosphorus compound such as phosphoricacid ester to impart flame retardance. For example, the proposedflame-retardant resin compositions include a resin compositioncomprising a blend of mixed resins, i.e. an aromatic polycarbonate andrubber reinforced styrene resin, with triphenyl phosphate andpolytetrafluoroethylene (PTFE) (JP-B-9-19003) and a resin compositioncomprising a blend of mixed resins, i.e. an aromatic polycarbonate andrubber reinforced styrene resin, with an oligomer of phosphoric acidester and PTFE (NL 8802346). These methods, however, entail variousproblems in terms of properties of plastics and processability thereof.Stated more specifically, the phosphoric acid ester has a low meltingpoint and poor compatibility with resins so that the resin compositionis given low heat resistance, and that the phosphoric acid ester oozesout from the resin in the molding process, thereby soiling the mold andbecoming vaporized. JP-A-5-1079 and U.S. Pat. No. 5,122,556 disclosetechniques for preparing a flame-retardant resin by mixing athermoplastic resin with a crystalline powder of aromatic diphosphateflame retardant. The disclosed methods, however, failed to produce aresin composition which is satisfactory both in properties and inprocessability. Since the phosphoric acid esters used in thesetechniques have an activity to plasticize the resin, the techniquesessentially use PTFE as a drip inhibitor (for inhibiting dripping oflive charcoal in burning) and therefore failed to produce asubstantially halogen-free flame-retardant resin composition.

Techniques for rendering plastics flame-retardant by mixing plasticswith a phosphazene compound as a flame retardant are disclosed inliterature. For example, it is proposed to provide a flame-retardantresin composition comprising a polycarbonate resin and a phosphazenecompound admixed therewith (JP-A-51-37149), a flame-retardant resincomposition comprising a phosphazene compound and a polycarbonatecompound or a mixture of the same and other thermoplastic resin(JP-A-7-292233), and a flame-retardant resin composition comprising aphosphazene compound and a mixture of an aromatic polycarbonate resinand a rubber reinforced styrene resin (JP-A-9-53009). When a phosphazenecompound is added to the resin, the flame retardance is enhanced asclear from the increase of limiting oxygen index (LOI). Yet, problemsremain unresolved since the phosphazene compound used has a low meltingpoint, and the resin composition is lowered in heat deformationtemperature, heat resistance and mechanical properties. Further, sincePTFE is essentially used as the drip inhibitor, a substantiallyhalogen-free flame-retardant resin composition has not been obtained.

An object of the present invention is to provide a flame-retardant resinwhich is molded without bleed of flame retardant and which neitherreduces the heat deformation temperature of flame-retardant resincomposition nor impairs the heat resistance and mechanical propertiesthereof, its composition and a process for preparing the same.

Another object of the invention is to provide a flame-retardant resinprepared without essential use of PTFE as the drip inhibitor and whichis substantially free of halogen, its composition and a process forpreparing the same.

DISCLOSURE OF THE INVENTION

The present invention provides a flame-retardant resin compositioncomprising a phosphazene flame retardant and a polyester resin, whereinthe flame retardant is bonded to the molecules of the polyester resinvia the ester group thereof.

Preferred embodiments of the invention are as follows.

(1) A flame-retardant resin comprising a phosphazene flame retardant anda polyester resin, wherein the flame retardant is bonded to themolecules of the polyester resin via the ester group thereof.

(2) A flame-retardant resin comprising a phosphazene flame retardant anda polyester resin, wherein ester exchange reaction is carried out usingthe flame retardant in an amount of 0.1 to 100 parts by weight per 100parts by weight of the polyester resin.

(3) A process for preparing a flame-retardant resin comprising aphosphazene flame retardant and a polyester resin, the processcomprising conducting ester exchange reaction between the flameretardant and the polyester resin in a molten state.

(4) A process for preparing a flame-retardant resin comprising aphosphazene flame retardant and a polyester resin, wherein thephosphazene flame retardant is at least one species selected from cyclicphosphazene compounds and straight-chain phosphazene compounds asdefined in claim 2.

The present inventors found the following. A reactive phosphazenecompound as the flame retardant is subjected to ester exchange reactionwith a polyester resin to bond to the molecules of polyester resin viathe ester group thereof without vaporization or loss of retardant. Usingthe obtained resin, a flame-retardant resin composition excellent inheat resistance and mechanical properties is produced without bleedingthe flame retardant in the molding process and without reducing the heatdeformation temperature of the resin composition. The present inventionwas completed based on the above-mentioned novel finding.

According to the present invention, a phosphazene flame retardant isreacted with a polyester resin to give a flame-retardant polyester resincontaining the phosphazene flame retardant bonded to the molecules ofthe polyester resin via the ester group thereof. Then, a resincomposition containing such resin is provided.

The present invention will be described in more detail. First of all,the reactive phosphazene compound to be used in the invention will bedescribed.

The phosphazene compound to be used in the invention is a compoundrepresented by the formula (I).

wherein n is the number of repetition, X and Y are independently O, S,NH or NR³ group wherein R³ is alkyl group having 1 to 4 carbon atoms, atleast one of R¹ and R² groups which are n in number is a group selectedfrom the groups shown below in chemical formula 2, and the remaining R¹and R² groups are independently the groups represented by chemicalformula 3, each of R⁴, R⁶ and R⁷ groups is hydrogen atom or alkyl grouphaving 1 to 4 carbon atoms, R⁵ is alkyl group having 1 to 4 carbonatoms, m is an integer of 1 to 10, and n is an integer of 3 to 25 whenthe phosphazene compound is a cyclic compound, or an integer of 3 to1000 when the phosphazene compound is a straight-chain compound.

Examples of phosphazene compounds useful in the invention arecyclotriphosphazene, cyclotetraphosphazene, clyclopentaphosphazenewherein mixing substitution is effected for hydroxyphenoxy group andphenoxy group and like cyclic phosphazene compounds or straight-chainphosphazene compounds. Specific examples of the cyclic phosphazenecompound wherein mixing substitution is effected for hydroxyphenoxygroup and phenoxy group are mono(hydroxyphenoxy)pentaphenoxycyclotriphosphaneze, di(hydroxyphenoxy)tetraphenoxy cyclotriphosphaneze,tri(hydroxyphenoxy)triphenoxy cyclotriphosphaneze,tetra(hydroxyphenoxy)diphenoxy cyclotriphosphaneze,penta(hydroxyphenoxy)monophenoxy cyclotriphosphaneze and likecyclotetraphosphaneze compounds, mono(hydroxy-phenoxy)heptaphenoxycyclotetraphosphaneze, di(hydroxyphenoxy)hexaphenoxycyclotetraphosphaneze, tri(hydroxyphenoxy)pentaphenoxycyclotetraphosphaneze, tetra(hydroxyphenoxy)tetraphenoxycyclotetraphosphaneze, penta(hydroxyphenoxy)triphenoxycyclotetraphosphaneze, hexa(hydroxyphenoxy)diphenoxycyclotetraphosphaneze, hepta(hydroxyphenoxy)monophenoxycyclotetraphosphaneze and like cyclotetraphosphaneze compounds,cyclopentaphosphaneze compounds wherein mixing substitution is effectedfor hydroxyphenoxy group and phenoxy group and like cyclic phosphazenecompounds. Further examples include straight-chain phosphazene compoundswherein mixing substitution is effected for hydroxyphenoxy group andphenoxy group. These compounds can be used in combination or as amixture of cyclic and straight-chain compounds or as an oligomer.

Selectable in place of the hydroxyphenoxy group of the phosphazenecompound are hydroxymethylphenoxy, hydroxyethylphenoxy,hydroxyethoxyphenoxy, methoxycarbonyl-phenoxy, ethoxycarbonylphenoxy,methoxycarbonylmethylphenoxy, methoxycarbonylethylphenoxy,methoxycarbonylvinylphenoxy, methoxycarbonyl(methoxy)phenoxy andmethoxycarbonyl-(dimethoxy)phenoxy. These groups may be those which maybe directly substituted with alkyl group having 1 to 4 carbon atoms onan aromatic ring. It is possible to select hydroxyphenylphenoxy,hydroxyphenoxyphenoxy, hydroxyphenylcumenyloxy,hydroxyphenylsulfonylphenoxy and hydroxyphenyl{methoxycarbonyl(methyl)propylphenoxy}. Also selectable are compoundswhich have S, NH or NR³ in place of the oxygen atom of said phenoxygroup. The groups may be a mixture of at least two kinds ofsubstituents.

The phosphazene compound of the invention can be prepared by variousprocesses. Usable as the raw material is, for example, a cyclic orstraight-chain phosphazene compound wherein n is an integer of 3 to 25such as hexachlorocyclotriphosphazene oroctachlorocyclotetra-phosphazene which can be prepared by reactingammonium chloride with phosphorus pentachloride at 120 to 130° C. asshown below in the formula (II). The solvents usable in the reactioninclude, for example, tetrachloroethane and chlorobenzene.

Dichlorophosphazene wherein n is an integer of 3 to 1000 which can beused as the straight-chain phosphazene compound in the invention can beprepared by taking out hexachlorocyclotriphosphazene from said mixtureof cyclic and straight-chain compounds, heating the phosphazene at 220to 250° C and subjecting it to ring opening polymerization as shownbelow in the formula (III).

The phosphazene compound of the invention can be prepared, for example,by reacting the above-obtained phosphazene compound with an alkali metalsalt of aromatic phenol admixed in a desired ratio. For example, metalsodium is added to hydroquinone monomethyl ether and phenol admixed in adesired ratio to give the corresponding sodium salt of phenol as shownbelow in chemical formula 6. Then, a cyclic and/or straight-chainphosphazene compound of the formula (II) wherein, for example, n is aninteger of 3 to 25 is added to the obtained sodium salt of phenol. Themixture is heated at 50 to 150° C. for 1 to 24 hours, and is subjectedto substitution reaction, thereby producing a phosphazene compoundhaving methoxyphenoxy group. The obtained phosphazene compound havingmethoxyphenoxy group is heated together with pyridine hydrochloride at200 to 220° C. for 1 to 3 hours, whereby the methoxy group is convertedto hydroxy group, giving the contemplated phosphazene compound havinghydroxyphenoxy group.

The contemplated phosphazene compound having hydroxyphenoxy group can beprepared by substitution reaction and deprotection reaction as describedabove. The reaction is feasible with or without a solvent. When asolvent is used, it is preferred to use, for example, benzene, toluene,xylene or tetrahydrofuran. For the efficiency of substitution reaction,tetrahydrofuran is more preferably used as the solvent. The substitutionreaction is completed if it is conducted at its reflux temperature forabout 5 hours. The deprotection reaction is feasible with use of areagent such as trimethylsilane iodide, aluminum trichloride, aluminumtribromide, boron tribromide, hydrogen bromide or hydrogen iodide aswell as with use of pyridine hydrochloride. Other known processes can beemployed.

Other processes than those described above include a process wherein acyclic and/or straight-chain dichlorophosphazene compound is reactedwith hydroquinone and an alkali metal salt of phenol and a processwherein dichlorophosphazene oligomer is reacted with an alkali metalsalt of hydroquinone monomethyl ether, and sequentially the reactionmixture is reacted with an alkali metal salt of aromatic phenol,followed by deprotection of methoxy group.

The contemplated phosphazene flame retardant having ester group can beprepared by the same substitution reaction.

The phosphazene flame retardant to be used is a compound having hydroxylor ester group at the end of molecules. From the viewpoints ofproduction process and ease of acquisition, it is suitable to usephosphazene oligomers (a mixture of cyclic and straight-chain compounds)wherein mixing substitution is effected for hydroxyphenoxy group andphenoxy group, hydroxyethylphenoxy group and phenoxy group,methoxycarbonylphenoxy group and phenoxy group, or ethoxycarbonylphenoxygroup and phenoxy group.

The foregoing phosphazene flame retardant is added alone or in suitablecombination to the polyester resin. The amount of the flame retardant tobe used is 0.1 to 100 parts by weight, preferably 1 to 50 parts byweight, per 100 parts by weight of the polyester resin. When the flameretardant is used in an amount within said range, flame retardance canbe economically imparted to a satisfactory extent and the obtained resincomposition is excellent in impact resistance and heat resistance.

Suitable polyester resins to be used in the invention are those having arelatively high melt temperature which are amenable to ester exchangereaction.

Examples of such polyester resins are polycarbonate, polyethyleneterephthalate, polyethylene naphthalate, polypropylene terephthalate,polybutylene terephthalate, polyhexamethylene terephthalate,polycyclohexanedimethylene terephthalate, poly(ethyleneterephthalate/cyclohexane-dimethylene terephthalate) copolymers,poly(ethylene terephthalate/ethylene isophthalate) copolymers, polyesterether, polyarylate, polyoxybenzoyl, polycaprolactone and likethermoplastic polyester resins.

The polyester resin useful in the invention may be used in mixture withother thermoplastic resins than polyester resins. Examples of otherthermoplastic resins than polyester resins are polyethylene,polypropylene, polyisoprene, polybutadiene, polystyrene,impact-resistant polystyrene, acrylonitrile-styrene resins (AS resins),acrylonitrile-butadiene-styrene resins (ABS resins), methylmethacrylate-butadiene-styrene resins (MBS resins), methylmethacrylate-acrylonitrile-butadiene-styrene resins (MABS resins),acrylonitrile-acryl rubber-styrene resins (AAS resins), polyalkyl(meth)acrylate, modified polyphenylene ether, polyamide, polyphenylenesulfide, polyether sulfone, polysulfone, polyether ketone, polyetherether ketone, polyamideimide, polyether imide, polyimide and liquidcrystal polymers. These resins can be used either alone or incombination.

The polycarbonate resins to be used in the invention may be optionallybranched thermoplastic aromatic polycarbonate polymers or copolymerswhich can be prepared by reacting phosgene or carbonic acid diester withan aromatic dihydroxy compound or a mixture of the same and a smallamount of at least trifunctional polyhydroxy compound. The polycarbonateresin has a viscosity-average molecular weight of 10,000 to 100,000,preferably 15,000 to 50,000 as calculated from a solution viscosity ofmethylene chloride at 25° C.

Examples of useful aromatic dihydroxy compounds arebis(hydroxyaryl)alkanes such as 2,2-bis(4-hydroxyphenyl)propane(bisphenol A), 2,2-bis(3,5-dibromo-4-hydroxyphenyl)propane(tetrabromobisphenol A), bis(4-hydroxyphenyl)methane,1,1-bis(4-hydroxyphenyl)ethane, 2,2-bis(4-hydroxyphenyl)butane,2,2-bis(4-hydroxyphenyl)octane,2,2-bis(4-hydroxy-3-methylphenyl)propane,1,1-bis(3-t-butyl-4-hydroxyphenyl)propane,2,2-bis(4-hydroxy-3,5-dimethylphenyl)propane,2,2-bis(3-bromo-4-hydroxyphenyl)propane,2,2-bis(3,5-dichloro-4-hydroxyphenyl)propane,2,2-bis(3-phenyl-4-hydroxyphenyl)propane,2,2-bis(3-cyclohexyl-4-hydroxyphenyl)propane,1,1-bis(4-hydroxyphenyl)-1-phenylethane andbis(4-hydroxyphenyl)diphenylmethane; bis(hydroxyaryl)cycloalkanes suchas 1,1-bis(4-hydroxyphenyl)cyclopentane and1,1-bis(4-hydroxyphenyl)cyclohexane; dihydroxydiaryl ethers such as4,4′-dihydroxydiphenyl ether and 4,4′-dihydroxy-3,3′-dimethyldiphenylether; dihydroxydiaryl sulfides such as 4,4′-dihydroxydiphenyl sulfideand 4,4′-dihydroxy-3,3′-dimethyldiphenyl sulfide; dihydroxydiarylsulfoxides such as 4,4′-dihydroxydiphenyl sulfoxide and4,4′-dihydroxy-3,3′-dimethyldiphenyl sulfoxide; dihydroxydiaryl sulfonessuch as 4,4′-dihydroxydiphenyl sulfone and4,4′-dihydroxy-3,3′-dimethyldiphenyl sulfone; hydroquinone, resorcin and4,4′-dihydroxydiphenyl.

These aromatic dihydroxy compounds can be used either alone or incombination. Of the above examples, 2,2-bis(4-hydroxyphenyl)propane issuitable to use.

The branched aromatic polycarbonate resin can be prepared by concomitantuse of at least trifunctional polyhydroxy compound. Examples of suchpolyhydroxy compounds 1,1-bis(3-t-butyl-are phloroglycine,2,6-dimethyl-2,4,6-tri(4-hydroxyphenyl)-3-heptene,4,6-dimethyl-2,4,6-tri(4-hydroxyphenyl)-2-heptene,1,3,5-tri(2-hydroxyphenyl)benzene, 1,1,1-tri(4-hydroxyphenyl)ethane,2,6-bis(2-hydroxy-5-methylbenzyl)-4-methylphenol and α, α′,α″-tri(4-hydroxyphenyl)-1,3,5-triisopropyl-benzene. Further examplesinclude 3,3-bis(4-hydroxyaryl)oxyindole(isatinbisphenol),5-chloroisatin-bisphenol, 5,7-dichloroisatinbisphenol and5-bromoisatin-bisphenol.

In the case of the polycarbonate prepared using phosgene, a chainterminator or a chain transfer agent may be used. Examples of the chainterminator or the chain transfer agent are phenol, p-t-butylphenol,tribromophenol, long-chain alkylphenol, hydroxybenzoic acid alkyl ester,alkyl ether phenol and like aromatic phenols, methanol, butanol and likealiphatic alcohols, mercaptane and phthalic acid imide. Further examplesinclude aliphatic or aromatic carboxylic acid chloride and aliphatic oraromatic carboxylic acid. These polycarbonate resins can be used eitheralone or in combination.

The phosphazene flame retardant of the invention, when mixed alone witha molten polyester resin before molding, causes ester exchange reactionat the ester linkage portion of molecules of polyester resin and can befixed to the resin by ester linkage. When required, a catalyst for esterexchange reaction can be added to further accelerate the ester exchangereaction.

There is no limitation on the kind of catalysts for ester exchangereaction insofar as they are used in this field. Examples of usefulcatalysts are lithium hydroxide, sodium hydroxide, potassium hydroxide,calcium hydroxide and like hydroxides of alkali metals or alkaline earthmetals; tin chloride, zinc chloride, ferric chloride, lead chloride andlike halogenated transition metals; aluminum lithium hydride, sodiumboron hydride, tetramethylammonium boron hydride and like alkali metalsalts, alkaline earth metal salts or quaternary ammonium salts of boronor aluminum hydrides; lithium hydride, sodium hydride, calcium hydrideand like hydrides of alkali metals or alkaline earth metals; lithiummethoxide, sodium methoxide, calcium methoxide and like alkoxides ofalkali metals or alkaline earth metals; lithium phenoxide, sodiumphenoxide, magnesium phenoxide, LiO—Ar—OLi, NaO—Ar—ONa (Ar=aryl group)and like aryloxides of alkali metals or alkaline earth metals; lithiumacetate, sodium acetate, calcium acetate, sodium benzoate and likeorganic acid salts of alkali metals or alkaline earth metals; zincoxide, zinc acetate, zinc phenoxide and like zinc compounds; boronoxide, boric acid, sodium borate, trimethyl borate, tributyl borate,triphenyl borate, ammonium borates or phosphonium borates represented bythe formula (R⁷ R⁸ R⁹ R¹⁰) NB (R⁷ R⁸ R⁹ R¹⁰) or (R⁷ R⁸ R⁹ R¹⁰) PB (R⁷ R⁸R⁹ R¹⁰) wherein R⁷ R⁸ R⁹ R¹⁰ are independently hydrogen atom, alkylgroup having 1 to 10 carbon atoms, alkoxy group, cycloalkyl group having5 to 10 carbon atoms which constitutes the ring, carbocyclic aromaticgroup having 5 to 10 carbon atoms which constitutes the ring andcarbocyclic aralkyl group having 6 to 10 carbon atoms and like boroncompounds; silicon oxide, sodium silicate, tetraalkylsilicon,tetraarylsilicon, diphenylethylethoxysilicon, and like siliconcompounds; germanium oxide, germanium tetrachloride, germanium ethoxide,germanium phenoxide and like germanium compounds; tin oxide, dialkyltinoxide, dialkyltin carboxylate, tin acetate, tributyltin methoxide,butyltin triethoxide, ethyltin tributoxide and like tin compounds withalkoxy group bonded thereto, organotin compounds and like tin compounds;lead oxide, lead acetate, lead carbonate, basic carbonate, alkoxides oraryloxides of lead and organic lead and like lead compounds; quaternaryammonium salts, quaternary phosphonium salts, quaternary arsonium saltsand like onium salt compounds; antimony oxide, antimony acetate and likeantimony compounds; manganese acetate, manganese carbonate, manganeseborate and like manganese compounds; titanium oxide, alkoxides oraryloxides of titanium and like titanium compounds; zirconium oxide,ziconium acetate, alkoxides or aryloxides of zirconium, acetylacetone ofzirconium and like zirconium compounds.

These catalysts may be used either alone or in combination. The amountof the catalyst to be used is selected from the range of 10⁻⁵ to 10% byweight, preferably 10⁻³ to 1% by weight.

The ratio of ester exchange between the phosphazene flame retardant andthe polyester resin is usually 30% or more, more preferably 80% or more.Desirably the upper limit is as near as 100%, but usually 30 to 99%,preferably 80 to 98%.

The production process of the invention will be described below withreference to the drawing.

FIG. 1 is a schematic view showing the production process of theinvention by way of example wherein a melt of the polyester resin iskneaded and extruded to give pellets.

Referring to FIG. 1, indicated at 1 is a twin-screw kneader(kneader-type extruder); at 1 a, a hopper disposed at a rear portion ofthe kneader for introducing a resin; at 1 b, a hopper providedintermediately in the kneader; at 1 c, a screw accommodated in thekneader; at 1 d, a mold for producing strands, provided at the forwardend of the kneader; at 2, a water tank for cooling; and at 3, a cutter.

According to an illustrated embodiment, a polyester resin 4 as the rawmaterial is dried by preheating and is placed into a kneader 1 via ahopper 1 a at a rear portion of the kneader 1 wherein the polyesterresin 4 is heated to higher than the melt temperature of the resin 4(but below the decomposition temperature thereof) to become melted andis kneaded by a screw 1 c. A mixture 5 of a phosphazene flame retardantand a catalyst for ester exchange reaction is charged into the kneader 1via a hopper 1 b arranged intermediately. The mixture 5 is uniformlykneaded together with the molten polyester resin 4 by the screw 1 c andis forced out as a rope-shaped product from a mold 1 d. The moldedproduct is taken out while cooled in the cooling water tank 2, and iscut to a predetermined size by the cutter 3.

When the phosphazene flame retardant and the catalyst for ester exchangereaction are kneaded as described above, the phosphazene flame retardantinduces ester exchange reaction at the ester linkage portion in themolecules of the resin or at the end of molecules thereof, whereby theflame retardant is bonded to the molecules of the resin by esterlinkage. The ester exchange reaction proceeds while the polyester resin4 is in a molten state.

When the pellets of polyester resin containing the phosphazene flameretardant are prepared by the above-mentioned process, the phosphazeneflame retardant is bonded by ester linakge and is immobilized in themolecules of polyester resin or at the end of molecules thereof withoutvaporization or dissipation of retardant from the pellets with time.

The polyester resin 4 suitable as the raw material has a relatively highmelt temperature and readily causes ester exchange reaction. Suitablepolyester resins are, for example, polycarbonate, polyethyleneterephthalate, polybutylene terephthalate, polyarylate, polyoxybenzoyl,polycaprolactone and like thermoplastic polyester resins.

The ester exchange reaction occurs between the polyester resin and thephosphazene flame retardant when, as described above, the polyesterresin is heated to higher than the melt temperature of the resin butlower than the decompostion temperature thereof to become melted. If apolycarbonate resin, for example, is used as the polyester resin, thepolycarbonate resin is heated at a temperature of about 230 to about330° C. in the kneader 1 to become melted. The time taken for the esterexchange reaction is slightly variable depending on the kind of flameretardant and kind of polyester resin used, but the reaction ispractically completed in approximately 1 to 15 minutes. In preparingpellets of resin composition as in the above-mentioned productionexample, the mixture 5 of flame retardant and catalyst for esterexchange is added to the melt of polyester resin 4 present in thekneader 1, and the blend is kneaded for about 1 to about 15 minutes andis forced out from the mold id at the forward end of the kneader 1. Inorder to carry out the foregoing operation, the position of intermediatehopper 1 b, the design of the screw and other extrusion conditionsshould be prearranged or considered for satisfactory practice of esterexchange reaction. In that case, a twin-screw extruder or kneader issuitably used.

In said embodiment, the polyester resin 4 is charged into the kneader 1through the hopper 1 a, and the mixture 5 of flame retardant andcatalyst for ester exchange, through the hopper 1 b. Optionally thepolyester resin 4 and the mixture 5 may be introduced together into thekneader 1 through any one of the hoppers, or the phosphazene flameretardant and the catalyst may be separately charged thereinto.

In the foregoing preparation example, the melt is forced out from themold id to give pellets after ester exchange reaction of the polyesterresin with the phosphazene flame retardant. It is possible, of course,to produce extrusion-molded products in various shapes such as resinplates, sheets, films or moldings of specific shapes. Further, a resinplate of two or three layers can be produced with use of a co-extruderor the like. Such multi-layer resin plate comprises a top layer composedof the polyester resin containing the phosphazene flame retardant bondedthereto by ester linkage, a second layer and a third layer each formedby co-extrusion molding of a polyester resin or other resin containingno or less amount of phosphazene flame retardant compared with the toplayer. Namely it is possible to produce a two- or three-layer resinplate having a layer of phosphazene-containing polyester resin on thesurface of the molded product.

Likewise in injection molding, a resin molded product can be producedwith little or no vaporization of flame retardant, when a melt ofpolyester resin is mixed with the flame retardant and the ester exchangecatalyst to induce ester exchange before the melt thereof is injectedinto the mold of injection molding machine.

The resin composition of the invention can exhibit a high flameretardant effect although free of a compound containing chlorine,bromine or like halogen elements as a flame-retardant component and cancontain a suitable combination of additives conventionally used forimparting flame retardance. Additives useful for rendering the resinflame-retardant are not limited insofar as they are useful in givingflame retardance. Examples of such additives are zinc oxide, tin oxide,iron oxide, molybdenum oxide, copper oxide, manganese dioxide and likemetallic oxides, aluminum hydroxide, magnesium hydroxide, zirconiumhydroxide, aluminum hydroxide treated with oxalic acid and magnesiumhydroxide treated with a nickel compound and like metal hydroxides,sodium carbonate, calcium carbonate, barium carbonate, sodiumalkylsulfonate and like alkali metal salts or alkaline earth metalsalts, chlorinated paraffin, perchlorocyclopentadecane,tetrabromobisphenol A, tetrabromobisphenol A epoxy oligomer or polymer,bis(tribromophenoxy)ethane, bis(tetrabromophthalimino)ethane and likeorganic chlorine or bromine compounds, antimony trioxide, antimonytetraoxide, antimony pentoxide, sodium antimonate and like antimonycompounds, triphenyl phosphate, tricresyl phosphate, trixylyl phosphate,cresyldiphenyl phosphate, xylyldiphenyl phosphate, tolyldixylylphosphate, (2-ethylhexyl)diphenyl phosphate and like phosphoric acidesters, hydroxyl-containing phosphoric acid ester, resorcinolbis(diphenyl)phosphate, hydroquinone bis(diphenyl)phosphate, bisphenol Abis(diphenyl)phosphate, resorcinol bis(dixylyl)phosphate, hydroquinonebis(dixylyl)phosphate, bisphenol A bis(ditolyl)phosphate, biphenolbis(dixylyl)phosphate, bisphenol A bis(dixylyl) phosphate and likecondensed phosphoric acid ester compounds, red phosphorus,halogen-containing phosphoric acid ester compounds, halogen-containingcondensed phosphoric acid ester compounds, phosphonic acid estercompounds, triphenylphosphine oxide, tritolylphosphine oxide and likephosphine oxide compounds, melamine, melamine cyanurate, melaminephosphate, melam, melem, melon, succinoguanamine, guanidine sulfamate,ammonium sulfate, ammonium phosphate, ammonium polyphosphate, alkylaminephosphate and like nitrogen-containing compounds, zinc borate, bariummetaborate, ammonium borate and like boron compounds, silicon polymer,silica and like silicon compounds and thermally expanding graphite.

These additives for flame retardance can be used either alone or incombination.

The resin composition of the invention admixed with afluorine-containing resin is likely to produce synergistic flameretardant effects, for example, the prevention of dropping the resinmelted by ignition. There is no limitation on the kind of suchfluorine-containing resins insofar as they are fluorinated polymers.Preferred resins are polymers having fluorine atoms bonded directly tothe main chain of polymer. Examples of useful fluorine-containing resinsare poly(tetrafluoroethylene), poly(chlorotrifluoroethylene),poly(vinylidene fluoride), tetrafluoroethylene-hexafluoropropylenecopolymers, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymersand tetrafluoroethylene-ethylene copolymers. These fluorine-containingresins can be used in any of forms such as emulsions, suspensions,microfibrils, powders or granules. The fluorine-containing resins can beused either alone or in combination.

Optionally the resin composition of the invention may contain a suitablecombination of additives for resins and fillers in the ranges of kindsand amounts which do not deteriorate the properties of the resincomposition. Examples of useful additives for resins are UV absorbers,light stabilizers, antioxidants, light screens, metal inactivatingagents, light extinguishers, heat resistance stabilizers, lubricants,mold release agents, coloring agents, antistatic agents, age resistors,plasticizers, impact strength modifiers and compatibilizers.

Examples of useful fillers are mica, kaolin, talc, silica, clay, calciumcarbonate, calcium sulfate, calcium silicate, glass beads, glassballoons, glass flakes, glass fibers, fibrous alkali titanate, fibroustransition metal salts of boric acid, fibrous alkaline earth metal saltsof boric acid, zinc oxide whiskers, titanium oxide whiskers, magnesiumoxide whiskers, gypsum whiskers, aluminum silicate whiskers, calciumsilicate whiskers, silicon carbide whiskers, titanium carbide whiskers,silicon nitride whiskers, titanium nitride whiskers, carbon fibers,alumina fibers, alumin-silica fibers, zirconia fibers, quartz fibers andmetal fibers. Typical examples of fibrous alkali metals of titanic acid,fibrous transition metal salts of boric acid and fibrous alkaline earthmetal salts of boric acid are potassium titanate fibers, aluminum boratefibers and magnesium borate fibers. These additives and fillers can beused either alone or in combination.

The thus-obtained resin composition can be used in industrial fieldsincluding the fields of electricity, electron, communications,agriculture, forestry, fisheries, mining, construction, foods, fibers,clothes, medical services, coal, petroleum, rubbers, leathers,automobiles, precision machines, timbers, furniture, printing andmusical instruments. For example, the resin composition of the inventioncan be used for printers, personal computers, word processors,keyboards, PDA (personal digital assistants), telephones, facsimilemachines, copiers, ECR (electronic cash registers), desk-topcalculators, electronic notebooks, electronic dictionaries, cards,holders, stationeries, business machines, office automation machines,washing machines, refrigerators, vacuum cleaners, electronic ovens,illuminators, game machines, irons, domestic electrical appliances suchas electrical foot warmers, television sets, VTR, video cameras, digitalcameras, radio-casette players, tape recorders, mini-discs, CD players,PD (phase change & dual function), DVD, speakers, liquid crystaldisplays and like audiovisual devices, connectors, relays, condensers,switches, printed boards, coil bobbins, semi-conductor sealers,electrical wires, cables, transformers, deflecting yokes, distributingboards, electrical or electronic components for watches or the like andcommunications equipment. The resin composition of the invention findsapplications in a wide variety of other products including seats(stuffings, covering materials and the like), belts, ceiling materials,convertible top materials, armrests, door trims, rear package trays,carpets, mats, sunvisors, wheel covers, mattress covers, air bags,insulators, hand straps, strap strips, electrical wire-coatingmaterials, electrical insulating materials, coating compositions,coating materials, covering materials, floor materials, corner walls,deck panels, covers, veneer boards, ceiling boards, partition boards,side walls, carpets, wall papers, wall-decorating materials, exteriortrims, interior trims, roof materials, sound-absorbing materials,heat-insulating materials, sash materials and other materials forautomobiles, vehicles, ships and aircraft, building materials, clothes,curtains, sheets, plywoods, synthetic fiber boards, carpets, doormats,sheets, buckets, hoses, containers, spectacles, bags, cases, goggles,ski goods, rackets, tents, musical instruments, toys and other goods fordaily use or for sports and leisure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a view schematically showing the production process of theinvention by way of example.

FIG. 2 shows a distribution curve of molecular weight of a test piece(1) according to the measurement by GPC. The symbol “M” indicated besidethe ordinate axis on the right side of the drawing is short formolecular weight.

FIG. 3 shows a distribution curve of molecular weight of a test piece(1′) before kneading the melt according to the measurement by GPC.

FIG. 4 shows a distribution curve of molecular weight of a comparativetest piece (51) according to the measurement by GPC.

BEST MODE OF CARRYING OUT THE INVENTION

The present invention will be described in more detail with reference tothe following examples to which, however, the present invention is notlimited at all.

EXAMPLE 1

Dry-blended were 100 parts by weight of an aromatic polycarbonate resin,12 parts by weight of a phosphazene flame retardant having the followingstructure and 0.03 part by weight of dibutyltin oxide as a catalyst forester exchange reaction. UPIRON S-2000 (brand name for a product ofMitsubishi Engineering Plastics Co., Ltd.) was used as the aromaticpolycarbonate resin (the same hereinafter).

The obtained blend was charged into an extrusion kneader and was heatedto 270° C. to obtain a melt. Then the melt was kneaded and was forcedout from the kneader after ester exchange reaction for about 3 minutes,whereby a test piece (1) for use in the following tests was prepared.

The test piece (1) was checked as described below to see whether thephosphazene flame retardant having reactive group was melted and kneadedtogether with the polyester resin, whereby ester exchange reaction wasinduced to react the flame retardant with the resin. A phosphazene flameretardant free of reactive group was used as a comparative sample.

Confirmation of Reaction

The test piece (1) obtained in Example 1 was dissolved intetrahydrofuran. Then the distribution of molecular weight of test piece(1) was measured by a gel permeation chromatography (GPC) deviceequipped with a differential refractometer. For comparison with the testpiece of Example 1, a flame retardant free of reactive group was blendedwith the polycarbonate resin as described later in Comparative Example 1in the same proportions as in Example 1, and the blend was melted andkneaded to give a comparative test piece (51) which did not undergoester exchange reaction. The distribution curve of molecular weight ofthe test piece (51) based on the measurement by GPC is as shown in FIG.4 wherein the peak (b) of flame retardant appeared on the side of lowmolecular weight (right side on the abscissa axis). On the other hand,the curve distribution of molecular weight of the test piece (1)obtained in Example 1 based on the measurement by GPC is as shown inFIG. 2 wherein the peak (a) of flame retardant appeared substantially atthe same eluation time as the peak (b) of retardant not involving esterexchange reaction but with a reduced detection intensity. The loweredpeak (a) presumably shifted and appeared as the peak (d) on the side ofhigh molecular weight (left side on the abscissa axis) . Namely, thereaction of flame retardant with the polycarbonate made the flameretardant into a high molecular weight one, resulting in shift of thepeak. Indicated at (d) is the peak of reacted portion and at (a), thepeak of unreacted portion. Subsequently the test piece (1) obtained inExample 1 was purified to remove the unreacted flame retardant. Then itwas confirmed by FT (Fourier Transform) -IR, ¹H-NMR and ¹³C-NMR whetherthe flame retardant was bonded to the polycarbonate by ester linkage.This also confirmed that the peak (d) did not indicatehomopolymerization of flame retardant alone.

The test piece (1) was also checked according to the test methoddescribed below to determine the quantity ratio (residue ratio) betweenthe phosphazene flame retardant existing as unreacted before kneadingthe melt and the phosphazene flame retardant remaining unreacted afterkneading the melt. The flame retardant was found to have performed theester exchange reaction at a residue ratio of about 6%.

Method of Measuring Residue Ratio

The residue ratio was confirmed using a GPC device as in theconfirmation of reaction as described above. The blend which did notundergo ester exchange reaction before kneading the melt in Example 1was taken as a test piece (1′). The distribution curve of molecularweight of the test piece (1′) according to the measurement by GPC is asshown in FIG. 3 wherein the peak (c) of flame retardant appeared on theside of low molecular weight (right side on the abscissa axis). On theother hand, the distribution curve of molecular weight of the test piece(1) involving kneading the melt in Example 1 according to themeasurement by GPC is as shown in FIG. 2 wherein the peak (a) of flameretardant appeared substantially at the same eluation time as the peak(c) of retardant not involving ester exchange reaction but with anexceedingly reduced detection intensity. The lowered peak (a) presumablyshifted and appeared at the position of the peak (d) on the side of highmolecular weight (left side on the abscissa axis) . Namely, the reactionof flame retardant and polycarbonate made the flame retardant into ahigh molecular weight one, resulting in shift of the peak. Indicated at(a) and (c) are the peaks of unreacted portion; at (d), the peak ofreacted portion; and at (e), the peak of resin portion. The residueratio was calculated from the area of peaks (a), (c), (d) and (e) by thefollowing equation.

Residue ratio (%)=[(a)/{(d)+(a)}]/[(c)/{(e)+(c)}]×100

The test piece (1) was subjected to a burning test by the test method ofUL-94. The Izod impact strength and heat deformation temperature weremeasured and accelerated weathering test was conducted according to thefollowing methods.

Burning Test

The burning test was carried out by a vertical flame test method asprescribed in UL-94. The result was taken as an index of flameretardance. (The test piece had a thickness of {fraction (1/16)} inch.)

Izod Impact Strength

The Izod impact strength was determined at 23° C. by a method inaccordance with JIS K-7210 and the result was taken as an index ofimpact resistance. (The test piece had a thickness of ⅛ inch and wasV-notched.)

Heat Deformation Temperature

The heat deformation temperature was determined by the method as definedin ASTM D-648 and the result was taken as an index of heat resistance.

Accelerated Weathering Test

The accelerated weathering test was conducted using a sunshine carbonweather meter (Suga tester, WEL-SUN DCH Model, rainfall: 18 minutes/1cycle: 120 minutes) as an accelerated weathering tester. After 500 hoursof the test, the appearance of the test piece was visually evaluated.Also after 500 hours of the test, the burning test as defined in UL-94was performed to confirm the change of flame retardance.

Criteria for Evaluation of Appearance

∘: No change

Δ: The surface was blanched or discolored.

×: Cracked

When the polyester resin containing the phosphazene flame retardant wasmelted and kneaded to obtain the test piece (1), the phosphazene flameretardant did not scatter away or adhere to the mold. In Examples 2 to18 to be described below, there was no scatter or adhesion ofphosphazene flame retardant to the mold.

EXAMPLE 2

A test piece (2) was prepared in the same manner as in Example 1 withthe exception of dry-blending 100 parts by weight of an aromaticpolycarbonate resin, 15 parts by weight of a phosphazene flame retardanthaving the following structure and 0.3 part by weight of zinc oxide as acatalyst. The test piece (2) was assessed for properties as done inExample 1. The results are shown in Table 1.

EXAMPLE 3

A test piece (3) was prepared in the same manner as in Example 1 withthe exception of dry-blending 100 parts by weight of an aromaticpolycarbonate resin, 12 parts by weight of cyclic and straight-chainphosphazene flame retardants represented by the following structuralformula wherein n is an integer of 3 to 25 and 0.2 part by weight offerric chloride as a catalyst. The test piece (3) was assessed forproperties as done in Example 1. The results are shown in Table 1.

EXAMPLE 4

A test piece (4) was prepared in the same manner as in Example 1 withthe exception of adding to 100 parts by weight of an aromaticpolycarbonate resin 12 parts by weight of cyclic and straight-chainphosphazene flame retardants represented by the following structuralformula wherein n is an integer of 3 to 25. The test piece (4) wasassessed for properties as done in Example 1. The results are shown inTable 1.

EXAMPLE 5

A test piece (5) was prepared in the same manner as in Example 1 withthe exception of adding 12 parts by weight of cyclic and straight-chainphosphazene flame retardants represented by the following structuralformula wherein n is an integer of 3 to 25 to 100 parts by weight of anaromatic polycarbonate resin. The test piece (5) was assessed forproperties as done in Example 1. The results are shown in Table 1.

EXAMPLE 6

A test piece (6) was prepared in the same manner as in Example 1 withthe exception of adding 12 parts by weight of phosphazene flameretardants represented by the following structural formula to 100 partsby weight of an aromatic polycarbonate resin. The test piece (6) wasassessed for properties as done in Example 1. The results are shown inTable 1.

EXAMPLE 7

A test piece (7) was prepared in the same manner as in Example 1 withthe exception of adding to 100 parts by weight of an aromaticpolycarbonate resin 12 parts by weight of straight-chain phosphazeneflame retardants represented by the following structural formula whereinn is an integer of 3 to 1000. The test piece (7) was assessed forproperties as done in Example 1. The results are shown in Table 1.

EXAMPLE 8

A test piece (8) was prepared in the same manner as in Example 1 withthe exception of adding to 100 parts by weight of an aromaticpolycarbonate resin 12 parts by weight of cyclic and straight-chainphosphazene flame retardants represented by the following structuralformula wherein n is an integer of 3 to 25. The test piece (8) wasassessed for properties as done in Example 1. The results are shown inTable 1.

EXAMPLE 9

A test piece (9) was prepared in the same manner as in Example 1 withthe exception of using no ester-exchange catalyst. The test piece (9)was assessed for properties as done in Example 1. The results are shownin Table 1.

EXAMPLE 10

A test piece (10) was prepared in the same manner as in Example 1 withthe exception of adding to 100 parts by weight of an aromaticpolycarbonate resin 12 parts by weight of cyclic and straight-chainphosphazene flame retardants represented by the following structuralformula wherein n is an integer of 3 to 25. The test piece (10) wasassessed for properties as done in Example 1. The results are shown inTable 1.

EXAMPLE 11

A test piece (11) was prepared in the same manner as in Example 1 withthe exception of adding to 100 parts by weight of an aromaticpolycarbonate resin 12 parts by weight of cyclic and straight-chainphosphazene flame retardants represented by the following structuralformula wherein n is an integer of 3 to 25. The test piece (11) wasassessed for properties as done in Example 1. The results are shown inTable 1.

EXAMPLE 12

Dry-blended were 75 parts by weight of an aromatic polycarbonate resin,25 parts by weight of ABS resin, 10 parts by weight of the phosphazeneflame retardants used in Example 1 and 0.3 part by weight of ferricchloride as an ester-exchange catalyst. A test piece (12) was preparedin the same manner as in Example 1 with the exception of charging theobtained blend into an extrusion kneader and heating to 230° C. toobtain a melt. The test piece (12) was assessed for properties as donein Example 1. The results are shown in Table 1.

EXAMPLE 13

A test piece (13) was prepared in the same manner as in Example 12 withthe exception of using the phosphazene flame retardants used in Example3 in place of the phosphazene flame retardants used in Example 12. Thetest piece (13) was assessed for properties as done in Example 1. Theresults are shown in Table 1.

EXAMPLE 14

A test piece (14) was prepared in the same manner as in Example 12 withthe exception of using the phosphazene flame retardants used in Example5 in place of the phosphazene flame retardants used in Example 12. Thetest piece (14) was assessed for properties as done in Example 1. Theresults are shown in Table 1.

EXAMPLE 15

Dry-blended were 70 parts by weight of an aromatic polycarbonate resin,30 parts by weight of polybutylene terephthalate resin, 10 parts byweight of the phosphazene flame retardants used in Example 1 and 0.2part by weight of ferric chloride as an ester-exchange catalyst. A testpiece (15) was prepared in the same manner as in Example 1 with theexception of charging the obtained blend into an extrusion kneader andheating to 230° C. to obtain a melt. The test piece (15) was assessedfor residue rate of the flame retardants, burning test by the testmethod of UL-94, izod impact strength, heat deformation temperature andweathering test. The results are shown in Table 1.

EXAMPLE 16

A test piece (16) was prepared in the same manner as in Example 15 withthe exception of using the phosphazene flame retardants used in Example3 in place of the phosphazene flame retardants used in Example 15. Thetest piece (16) was assessed for properties as done in Example 1. Theresults are shown in Table 1.

EXAMPLE 17

A test piece (17) was prepared in the same manner as in Example 15 withthe exception of using the phosphazene flame retardants used in Example5 in place of the phosphazene flame retardants used in Example 15. Thetest piece (17) was assessed for properties as done in Example 1. Theresults are shown in Table 1.

EXAMPLE 18

A test piece (18) was prepared in the same manner as in Example 1 withthe exception of not using an ester-exchange catalyst, dibutyltin oxide.The test piece (18) was assessed for properties as done in Example 1.The results are shown in Table 1.

COMPARATIVE EXAMPLE 1

A test piece (51) was prepared in the same manner as in Example 1 withthe exception of using the phosphazene flame retardants represented bythe following structural formula. The test piece (51) was assessed forproperties as done in Example 1. The results are shown in Table 1.

COMPARATIVE EXAMPLE 2

A test piece (52) was prepared in the same manner as in Example 1 withthe exception of using triphenyl phosphite in place of the phosphazeneflame retardants used in Example 1. The test piece (52) was assessed forproperties as done in Example 1. The results are shown in Table 1.

COMPARATIVES EXAMPLE 3

A test piece (53) was prepared in the same manner as in Example 1 usingresorcinol-cross linked condensed phosphoric acid diphenyl ester (brandname for a product of Daihachi Kagaku Kogyo K. K., a compound identicalwith CR 733S) in place of the phosphazene flame retardants used inExample 1. The test piece (53) was assessed for properties as done inExample 1. The results are shown in Table 1.

COMPARATIVE EXAMPLE 4

A test piece (54) was prepared in the same manner as in Example 1 usingresorcinol-crosslinked condensed phosphoric acid di(2,6-xylyl) ester(brand name for a product of Daihachi Kagaku Kogyo K. K., a compoundidentical with PX-200) in place of the phosphazene flame retardants usedin Example 1. The test piece (54) was assessed for properties as done inExample 1. The results are shown in Table 1.

COMPARATIVE EXAMPLE 5

A test piece (55) was prepared in the same manner as in Example 12 usingresorcinol-crosslinked condensed phosphoric acid diphenyl ester (brandname for a product of Daihachi Kagaku Kogyo K. K., a compound identicalwith CR 733S) in place of the phosphazene flame retardants used inExample 12. The test piece (55) was assessed for properties as done inExample 1. The results are shown in Table 1.

COMPARATIVE EXAMPLE 6

A test piece (56) was prepared in the same manner as in Example 15 usingresorcinol-crosslinked condensed phosphoric acid diphenyl ester (brandname for a product of Daihachi Kagaku Kogyo K. K., a compound identicalwith CR 733S) in place of the phosphazene flame retardants used inExample 15. The test piece (56) was assessed for properties as done inExample 1. The results are shown in Table 1.

TABLE 1 Weathering Test Residue UL-94 Izod Heat weathering UL-94 ratioflame Impact deformation test flame (%) retardance (kgf · cm/cm)temperature after 500 h retardance Ex. 1  6 V-0  82 135 ∘ V-0 Ex. 2  4V-0  88 133 ∘ V-0 Ex. 3  4 V-0  86 135 ∘ V-0 Ex. 4  7 V-0  89 130 ∘ V-0Ex. 5  3 V-0  85 133 ∘ V-0 Ex. 6  5 V-0  90 134 ∘ V-0 Ex. 7  4 V-0  83130 ∘ V-0 Ex. 8  5 V-0  86 130 ∘ V-0 Ex. 9  7 V-0  87 133 ∘ V-0 Ex. 10 4 V-0  81 135 ∘ V-0 Ex. 11  5 V-0  88 133 ∘ V-0 Ex. 12  5 V-0  60 110 ∘V-0 Ex. 13  4 V-0  58 105 ∘ V-0 Ex. 14  5 V-0  61 111 ∘ V-0 Ex. 15  5V-0 110 109 ∘ V-0 Ex. 16  5 V-0 112 108 ∘ V-0 Ex. 17  5 V-0 109 109 ∘V-0 Ex. 18 15 V-0  80 132 ∘ V-0 Com. Ex. 1 99 V-0  80 128 Δ V-0 Com. Ex.2 97 spec.out  49  98 x spec.out Com. Ex. 3 99 V-2  53 112 x spec.outCom. Ex. 4 98 V-2  50  93 x V-2 Com. Ex. 5 95 V-2 100 103 x spec.outCom. Ex. 6 98 spec.out 102 104 x spec.out

Table 1 shows that the resin compositions of the invention had awell-balanced combination of excellent flame retardance, impactresistance and heat resistance. On the other hand, the comparative testpiece (51) containing the phosphazene flame retardant incapable ofconducting ester exchange reaction and the comparative test pieces (52)to (56) containing the phosphoric acid ester flame retardants werelikely to vaporize with time, and became more degraded in propertiesafter irradiation for 1000 hours because the flame retardants wereunable to bond to the molecules of polyester resin by ester linkage. Incontrast, the test pieces (1) to (18) containing the phosphazene flameretardants capable of conducting ester exchange according to theinvention were such that a major portion of flame retardant was fixed tothe molecules of polyester resin by ester linkage and exhibitedexcellent flame retardance without causing change in appearance even byexposure to irradiation for 1000 hours. When the phosphoric acid estercompounds were used as the flame retardant in Comparative Examples 2 to6, the obtained resin compositions showed low flame retardance and poorheat resistance, and therefore were low in commercial value.

INDUSTRIAL APPLICABILITY

As apparent from the foregoing description and the test results, theresins containing phosphazene flame retardants according to theinvention can retain a high flame retardance for a prolonged term withlittle or no vaporization with time and is excellent in all of flameretardance, impact resistance, processability and other properties sincethe phosphazene flame retardant having hydroxy or ester group isimmobilized to the molecules of the resin by ester linkage on esterexchange of high reactivity. Using the flame-retardant resin of theinvention, a flame-retardant thermoplastic resin material free ofbromine, chlorine or like halogen elements can be produced. Therefore,the present invention is industrially very valuable.

The production process of the invention can be carried out with use ofvarious conventional general-purpose molding machines merely by adding aphosphazene flame retardant having hydroxy group or ester group to thepolyester resin and heating the blend to obtain a melt. Consequently thepresent invention eliminates a need for newly installing a specialmolding machine or device and is hence economical. In addition, theprocess of the invention can mass-produce highly flame-retardant moldedproducts with high efficiency.

What is claimed is:
 1. A flame-retardant resin composition, comprising aphosphazene flame retardant and a polyester resin, wherein the flameretardant is bonded to the polyester resin by an ester group thereof,wherein the phosphazene flame retardant is a phosphazene of formula (I)

wherein n is an integer, X and Y are independently, O, S, NH or NR³,wherein R³ is an alkyl group having 1 to 4 carbon atoms, at least one ofR¹ and R², which are n in number, is a group selected from the groupconsisting of formula (2)

 and the remaining R¹ and R² groups are independently, a group selectedfrom the group consisting of formula (3)

wherein each of R⁴, R⁶ and R⁷ is a hydrogen atom or alkyl group having 1to 4 carbon atoms, R⁵ is an alkyl group having 1 to 4 carbon atoms, m isan integer of 1 to 10, and n is an integer of 3 to 25 when thephosphazene is a cyclic compound, or an integer of 3 to 1000 when thephosphazene is a straight-chain compound.
 2. A flame-retardant resincomprising a phosphazene flame retardant and a polycarbonate resin,wherein the flame retardant is bonded to molecules of the polycarbonateresin by an ester group thereof.
 3. A flame retardant resin comprising aphosphazene flame retardant and a polycarbonate resin, wherein the flameretardant resin is obtained by an ester exchange reaction between theflame retardant and the polycarbonate resin in an amount of 0.1 to 100parts by weight per 100 parts by weight of the polycarbonate resin.
 4. Aprocess for preparing a flame-retardant resin comprising a phosphazeneflame retardant and a polyester resin, the process comprising conductingan ester exchange reaction between the flame retardant and the polyesterresin in a molten state, wherein the phosphazene is free of halogenatoms.
 5. A process for preparing a flame-retardant resin comprising aphosphazene flame retardant and a polyester resin, the processcomprising conducting an ester exchange reaction between the flameretardant and the polyester resin in a molten state, wherein thephosphazene flame retardant is at least one species selected from thegroup of cyclic phosphazene compounds and straight-chain phosphazenecompounds of formula (I)

wherein n is an integer, X and Y are independently, O, S, NH, and NR³,wherein R³ is an alkyl group having 1 to 4 carbon atoms, at least one R¹and R², which are n in number, is a group selected from the groupconsisting of formula (2)

 and the remaining R¹ and R² groups are independently, a group selectedfrom the group consisting of formula (3)

wherein each of R⁴, R⁶ and R⁷ is a hydrogen atom or alkyl group having 1to 4 carbon atoms, R⁵ is an alkyl group having 1 to 4 carbon atoms, m isan integer of 1 to 10, and n is an integer of 3 to 25 when thephosphazene is a cyclic compound, or an integer of 3 to 1000 when thephosphazene is a straight-chain compound.